(1) Field of the Invention
The present invention relates to a learning-correcting method and apparatus and a self-diagnosis method and apparatus in a fuel supply control system of an internal combustion engine. More particularly, the present invention relates to a learning-correcting method and apparatus for correcting deviations of an air-fuel ratio by respective factors in a fuel supply control system provided with a function of the feedback control of the air-fuel ratio and a self-diagnosis method and apparatus for diagnosing disorder of the fuel supplys control system based on the results of this correction by the respective factors.
(2) Description of the Related Art
As the known fuel supply control system of an internal combustion engine, the following system can be mentioned.
A sucked air flow quantity Q is detected as the quantity of the state of sucked air, and based on sucked air detected values and the detected value of the engine revolutions N, the basic fuel supply quantity Tp is computed. Then, this basic fuel supply quantity Tp is corrected, based on various correction coefficients COEF set by various driving state factors, such as the engine temperature represented by the cooling water temperature, an air-fuel ratio feedback correction coefficient LMD set based on the air-fuel ratio in the air-fuel mixture detected through the oxygen concentration in the exhaust gas and a correction proportion Ts for correcting the change of the opening or closing delay of the fuel injection valve by the battery voltage, to compute a final fuel supply quantity (=Tp.times.COEF.times.LMD.times.Ts). Fuel in this computed quantity is supplied to the engine through a fuel injection valve or the like (see Japanese Unexamined Patent Publication No. 60-240840).
The air-fuel ratio feedback correction coefficient LMD is set, for example, by proportional-integral control. When the actual air-fuel ratio detected, based on the oxygen concentration in the exhaust gas detected by an oxygen sensor, is rich (lean) as compared with the target air-fuel ratio (theoretical air-fuel ratio), the air-fuel ratio feedback correction coefficient LMD is first decreased (increased) by a proportion component P and then gradually decreased (increased) by and integration component I synchronously with the revolution of the engine or at the same frequency as that of the revolution of the engine. Thus, the actual air-fuel ratio is controlled in such a manner that reversal of the actual air-fuel ratio is repeated in the vicinity of the target air-fuel ratio.
In the above-mentioned fuel supply control system, when a deviation of the air-fuel ratio is caused, this deviation is detected by the oxygen sensor and the air-fuel ratio is feedback-controlled to the target air-fuel ratio. Accordingly, generation of the deviation of the air-fuel ratio can be judged by the feedback correction coefficient. However, since there are many factors causing the deviation of the air-fuel ratio, it is impossible to judge the factor actually causing the deviation of the air-fuel ratio.
As factors, causing the deviation of the air-fuel ratio, the leakage of air to the downstream side of the air flow meter for measuring the sucked air quantity, the deviation of the injection characteristics of the fuel injection valve and disorders of the pressure regulator for determining the pressure of the supplied fuel and the fuel pump can be mentioned. Patterns of the deviations of the air-fuel ratio caused by these factors are different from one another.
Accordingly, for example, even if the air-fuel ratio feedback correction coefficient LMD is learned for each of driving conditions classified by the engine load and revolution speed and a learning correction coefficient for each driving condition is set to correct the fuel supply quantity so that the air-fuel ratio obtained without the air-fuel ratio feedback correction coefficient LMD is brought close to the target air-fuel ratio, since the oxygen sensor generally detects the average air-fuel ratio in respective cylinders, especially if deviations of the injection characteristics are caused among the respective cylinders, it is impossible to obtain the target air-fuel ratio in any of the cylinders. Furthermore, since patterns of deviations of the air-fuel ratio for respective driving conditions by the factors are different from one another, attainment of a good correction cannot be expected in a driving condition where the learning frequency is low, and it is apprehended that a great gap of the air-fuel ratio is brought about by the difference of the learning frequency.